What is your favourite Windbg tip/trick? [closed]

My favorite is the command .cmdtree <file> (undocumented, but referenced in previous release notes). This can assist in bringing up another window (that can be docked) to display helpful or commonly used commands. This can help make the user much more productive using the tool.

Initially talked about here, with an example for the <file> parameter:http://blogs.msdn.com/debuggingtoolbox/archive/2008/09/17/special-command-execute-commands-from-a-customized-user-interface-with-cmdtree.aspx

Example:alt text http://blogs.msdn.com/photos/debuggingtoolbox/images/8954736/original.aspx

To investigate a memory leak in a crash dump (since I prefer by far UMDH for live processes).The strategy is that objects of the same type are all allocated with the same size.

• Feed the !heap -h 0 command to WinDbg's command line version cdb.exe (for greater speed) to get all heap allocations:

"C:\Program Files\Debugging Tools for Windows\cdb.exe" -c "!heap -h 0;q" -z [DumpPath] > DumpHeapEntries.log

• Use Cygwin to grep the list of allocations, grouping them by size:

grep "busy ([[:alnum:]]\+)" DumpHeapEntries.log \| gawk '{ str = $8; gsub(/\(|\)/, "", str); print "0x" str " 0x" $4 }' \| sort \| uniq -c \| gawk '{ printf "%10.2f %10d %10d ( %s = %d )\n", $1*strtonum($3)/1024, $1, strtonum($3), $2, strtonum($2) }' \| sort > DumpHeapEntriesStats.log

• You get a table that looks like this, for example, telling us that 25529270 allocations of 0x24 bytes take nearly 1.2 GB of memory.

   8489.52        707      12296 ( 0x3000 = 12288 )  11894.28       5924       2056 ( 0x800 = 2048 )  13222.66     846250         16 ( 0x2 = 2 )  14120.41     602471         24 ( 0x2 = 2 )  31539.30    2018515         16 ( 0x1 = 1 )  38902.01    1659819         24 ( 0x1 = 1 )  40856.38        817      51208 ( 0xc800 = 51200 )1196684.53   25529270         48 ( 0x24 = 36 )

• Then if your objects have vtables, just use the dps command to seek some of the 0x24 bytes heap allocations in DumpHeapEntries.log to know the type of the objects that are taking all the memory.

0:075> dps 3be7f7e83be7f7e8  000200063be7f7ec  090c01e73be7f7f0  0b40fe94 SomeDll!SomeType::`vftable'3be7f7f4  000000003be7f7f8  00000000

It's cheesy but it works :)

The following command comes very handy when looking on the stack for C++ objects with vtables, especially when working with release builds when quite a few things get optimized away.

dpp esp Range

Being able to load an arbitrary PE file as dump is neat:

windbg -z mylib.dll

Query GetLastError() with:

!gle

This helps to decode common error codes:

!error error_number